This invention relates to improvements in heart valves using autologous tissue held in place by anchors and an outer sheath. The heart valve can be constructed intraoperatively within a short time, typically 10 minutes.
Several types of heart valves are presently available for use in replacing diseased or malfunctioning heart valves in humans.
One form of heart valve is constructed from animal tissue, typically from bovine or porcine aortic valve tissue. These valves must typically be constructed in a laboratory well in advance of when they will be needed and then stored in an aldehyde solution. Skilled technicians are required to assemble these valves. The valves constructed from animal tissue have relatively short lifetimes. The short lifetimes are caused by two factors. First, there is an antigenic reaction by the body to the animal tissue which causes the tissue to calcify, making it inflexible and more susceptible to failure with time. Second, the tissue is often stored in glutaraldehyde before implantation to try to decrease the antigenic reaction. The aldehyde tends to tan the tissue to a leather-like consistency, which makes it wear out from the repeated stress of opening and closing.
Thus, although these animal tissue valves are widely used, most have to be replaced after about five to ten years. Replacing the valves poses risks to the patient, because a second open heart operation is then needed, with the attendant possibility of problems during the operation.
Mechanical heart valves are also available. These valves are made from hard, non-biological materials such as metals or ceramics. Although the mechanical heart valves are durable, the hard, non-biological surfaces on the valves tend to cause blood clots. The blood clots can cause heart attacks or strokes, and, as a result, patients with mechanical heart valves must take anticoagulant drugs. These drugs can lead to hemorrhagic complications. Also, patients on these drugs require frequent and lifelong laboratory tests of their clotting time.
Another type of heart valve, the autogenous tissue valve, is constructed with the patient""s own tissue. A number of patents for autologous tissue heart valves and methods of making autologous tissue heart valves have issued to Autogenics, assignee of this application, including U.S. Pat. Nos. 5,161,955 and 5,326,371.
This invention provides an improved apparatus and method for constructing an autologous tissue heart valve. A significant factor of the invention is that both the configuration of the autologous tissue and its means for attachment to the frame of the valve prevent deleterious stress on the tissue.
Accurate placement of the autologous tissue is provided by forming pericardium tissue taken from the patient into three separate tissue leaflets, each generally semi-circular shape and having a plurality of tissue anchor holes located along a tissue cusp line. The location of these tissue anchor holes correspond to tissue anchor hooks permanently attached to a tissue mounting frame.
These three leaves of tissue are placed sequentially on the tissue anchor hooks of the tissue mounting frame so as to be located completely around the circumference of the tissue mounting frame. An elastomeric sheath is stretched over the exterior of the tissue mounting frame. This sheath prevents the tissue from coming off the tissue anchor hooks and rests gently on the tissue around the cusp line such that the tissue forms a naturally closed valve.
A significant feature of this invention is that the manner in which the autologous tissue is supported prevents deleterious stress on the tissue. The tissue is thus not clamped between two unyielding members, but rather supported and retained by the combination of anchors mated in tissue anchor holes and the elastomeric sheath engaging a peripheral portion of the tissue leaflets between the elastomeric sheath member and the inner tissue mounting frame.
Another feature of the invention is that the tissue leaflets are formed to include sufficient extra tissue area to provide a physiologically representative coaptation line angle to thereby reduce the stretch in the tissue held in place by the sheath and thus further reduce the stress in the tissue.